In the torque demand control of an internal combustion engine for an automobile, more particularly, a gasoline engine, which has been conventionally proposed, requested torque to the internal combustion engine is determined from the acceleration operation amount by a driver. Subsequently, the air amount for realizing the requested torque is determined as a target air amount, and the throttle opening is determined in accordance with the target air amount.
Incidentally, the air amount that is controlled by a throttle affects the magnitude of the torque that is generated by fuel being combusted from a compression stroke to an expansion stroke. However, to be precise, the torque that is generated by an internal combustion engine is not determined only by the torque generated by combustion of the fuel. The value that is obtained by subtracting pump loss from the torque generated by combustion of the fuel is the torque that is generated by the internal combustion engine, namely, indicated torque of the internal combustion engine. Accordingly, in order to calculate the target air amount necessary for realization of the requested torque accurately, the pump loss that is generated from an exhaust stroke to an intake stroke is desirably taken into consideration.
The art of using pump loss in calculation of the target air amount in torque demand control is disclosed in, for example, Japanese Patent Laid-Open No. 2006-291803. According to the art that is disclosed in the literature, the pump loss is calculated based on a pressure difference between atmospheric pressure and an intake pipe, and the engine speed. Indicated requested torque is calculated by adding the pump loss to the requested torque, and the target air amount is calculated from the indicated requested torque.
However, the art disclosed in the above described literature has a problem. The art disclosed in the above described literature calculates the actual value of the pump loss from the actually measured value of the intake pipe pressure by the intake pipe pressure sensor, and uses the actual value of the pump loss in calculation of the target air amount. Since the intake pipe pressure changes in response to movement of the throttle, a change also occurs to the pump loss by the change of the intake pipe pressure at a time of a transient operation when the throttle is moving. Namely, by the throttle operations, the value of the pump loss that is used in calculation of the target air amount changes. Therefore, in the art disclosed in the above described literature, hunting occurs to the operation of the throttle at the time of a transient operation, and there arises the fear that control cannot be quickly performed to achieve the air amount that can realize the requested torque.